In this particular case, Vscode doesn't have the bug... Because it's responsible for this mess in the first place. LSP was first introduced in Vscode which is written in C++ and typescript, so they found it convenient to assume a UTF-16 encoding (as is native to Javascript). If LSP had originated elsewhere it'd probably use codepoint or UTF-8 byte offsets from the start.
Exactly. On a moral level that's obviously bad. But on a practical level that supports my decision to use VSCode - they got to define the standard such that everyone else has to work around their mess, making themselves have less problems.
